diff --git a/backend/genesys_devices.c b/backend/genesys_devices.c
index 1ec916a91..d8bc7ce53 100644
--- a/backend/genesys_devices.c
+++ b/backend/genesys_devices.c
@@ -1024,10 +1024,11 @@ static Genesys_Model hp3670c_model = {
   GPO_HP3670,
   MOTOR_HP3670,
       GENESYS_FLAG_14BIT_GAMMA
-    | GENESYS_FLAG_SEARCH_START
-    | GENESYS_FLAG_SKIP_WARMUP
+    | GENESYS_FLAG_NO_CALIBRATION    /* until fully supported */
+    /* | GENESYS_FLAG_SEARCH_START
     | GENESYS_FLAG_DARK_CALIBRATION
-    | GENESYS_FLAG_OFFSET_CALIBRATION
+    | GENESYS_FLAG_OFFSET_CALIBRATION until fully supported */
+    | GENESYS_FLAG_SKIP_WARMUP
     | GENESYS_FLAG_CUSTOM_GAMMA,
   GENESYS_HAS_NO_BUTTONS, /* no buttons supported */
   20,
diff --git a/backend/genesys_gl646.c b/backend/genesys_gl646.c
index d26f0593d..993b2e2cc 100644
--- a/backend/genesys_gl646.c
+++ b/backend/genesys_gl646.c
@@ -1484,11 +1484,16 @@ gl646_init_regs (Genesys_Device * dev)
       dev->reg[reg_0x20].value = 0x20;
       break;
     case CCD_HP2400:
-    case CCD_HP3670:
       dev->reg[reg_0x1e].value = 0x80;
       dev->reg[reg_0x1f].value = 0x10;
       dev->reg[reg_0x20].value = 0x20;
       break;
+    case CCD_HP3670:
+      dev->reg[reg_0x19].value = 0x2a;
+      dev->reg[reg_0x1e].value = 0x80;
+      dev->reg[reg_0x1f].value = 0x01;
+      dev->reg[reg_0x20].value = 0x50;
+      break;
       break;
     case CIS_XP200:
       dev->reg[reg_0x1e].value = 0x10;